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Re: John traveled the entire 50 km trip. If he travelled the first 20 km o [#permalink]
MathRevolution wrote:
[GMAT math practice question]

John traveled the entire 50 km trip. If he traveled the first 20 km of the trip at a constant rate 40 km per hour and the remaining trip at a constant rate 20 km per hour, what is his average speed, in km per hour?

A. 20 km/h
B. 23 km/h
C. 25 km/h
D. 26 km/h
E. 27 km/h



Average Speed= Total distance traveled/Total time taken
=50/(20/40+30/20)
=50/2=25
Answer C
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Re: John traveled the entire 50 km trip. If he travelled the first 20 km o [#permalink]
Expert Reply
=>
Ave Speed = ( Total Distance ) / ( Total Time )
The total distance = \(50 km\).
Total time is \(\frac{20}{40} + \frac{30}{20} = 0.5 + 1.5 = 2\)
The average speed is \(\frac{50}{2} = 25.\)
Therefore, the answer is C.

Answer : C
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Re: John traveled the entire 50 km trip. If he travelled the first 20 km o [#permalink]
MathRevolution wrote:
[GMAT math practice question]

John traveled the entire 50 km trip. If he traveled the first 20 km of the trip at a constant rate 40 km per hour and the remaining trip at a constant rate 20 km per hour, what is his average speed, in km per hour?

A. 20 km/h
B. 23 km/h
C. 25 km/h
D. 26 km/h
E. 27 km/h


Average speed = total distance / total time = 50 / (20/40 + 30/20) = 50 / (1/2 + 3/2) = 25
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Re: John traveled the entire 50 km trip. If he travelled the first 20 km o [#permalink]
MathRevolution wrote:
[GMAT math practice question]

John traveled the entire 50 km trip. If he traveled the first 20 km of the trip at a constant rate 40 km per hour and the remaining trip at a constant rate 20 km per hour, what is his average speed, in km per hour?

A. 20 km/h
B. 23 km/h
C. 25 km/h
D. 26 km/h
E. 27 km/h

Time for travelling first 20 Kms = 0.50 Hr
Time for travelling first 30 Kms = 1.50 Hr

Total time taken = 2.00 Hrs

So, Average speed in kmph is \(\frac{50}{2} = 25kmph\), Answer must be (C)
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Re: John traveled the entire 50 km trip. If he travelled the first 20 km o [#permalink]
Expert Reply
MathRevolution wrote:
[GMAT math practice question]

John traveled the entire 50 km trip. If he traveled the first 20 km of the trip at a constant rate 40 km per hour and the remaining trip at a constant rate 20 km per hour, what is his average speed, in km per hour?

A. 20 km/h
B. 23 km/h
C. 25 km/h
D. 26 km/h
E. 27 km/h


We can use the equation: average = total distance/total time

50/(20/40+ 30/20)

50/(1/2 + 3/2)

50/(4/2) = 50/2 = 25

Answer: C
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Re: John traveled the entire 50 km trip. If he travelled the first 20 km o [#permalink]
Can harmonic mean only be used when the distance travelled is the same?
Using harmonic mean here got 26.666km/h
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Re: John traveled the entire 50 km trip. If he travelled the first 20 km o [#permalink]
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Re: John traveled the entire 50 km trip. If he travelled the first 20 km o [#permalink]
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